Film deposition apparatus, film deposition method, and computer program storage medium

ABSTRACT

When alternately performing a film deposition step where a silicon-containing gas and O 3  gas are alternately supplied to a substrate on a susceptor by rotating the susceptor thereby to forma thin film of the reaction product, and an alteration step where the reaction product is altered by irradiating plasma to the substrate, plasma intensity of the plasma is changed during film deposition. Specifically, the plasma intensity is lower when a thickness of the thin film is small (or at an initial stage of the film deposition—alteration step), and is increased as the thin film becomes thicker (or as the number of the film deposition steps is increased). Alternatively, the plasma intensity is higher when the thin film is relatively thin and then reduced.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority of Japanese PatentApplication No. 2010-191247, filed on Aug. 27, 2010 with the JapanesePatent Office, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a film deposition apparatus and a filmdeposition method, where two or more kinds of reaction gases arealternately supplied to a surface of a substrate under vacuum, therebyto deposit a thin film on the substrate, and a storage medium thatstores a computer program that causes the film deposition apparatus toperform the film deposition method.

2. Description of the Related Art

When, for example, a silicon oxide film is deposited on a substrate suchas a semiconductor wafer made of silicon (referred to as a waferhereinafter) having patterns including pillar-shaped or line-shapedconvex portions formed on the surface of the wafer, a film depositionmethod called an Atomic Layer Film deposition (ALD) method or aMolecular Layer Film deposition (MLD) method may be used. Specifically,a thin film of silicon oxide is formed on the wafer by alternatelysupplying an organic material gas containing silicon and an oxidizinggas to the wafer under vacuum, thereby to accumulate an atomic layer ora molecular layer made of the reaction product. The thin film formed bysuch a film deposition method may have lower density because organicsubstances originating from the organic material gas remain in the thinfilm. This may be caused in part because a film deposition temperatureof the film deposition method is relatively lower than that of aconventional Chemical Vapor Film deposition (CVD) method.

Then, densification of the thin film has been investigated by exposingthe wafer to plasma of an alteration gas including oxygen (O₂), therebyto alter or densify the reaction product. However, when the thin filmbecomes thicker than a film thickness (or depth) through which theplasma can penetrate, a lower part of the thin film cannot be altered.On the other hand, when the thin film is thinner than the penetrationdepth, the plasma can reach an underlying layer of the thin film, sothat an upper surface of the underlying layer made of, for example,silicon may be oxidized, as shown in FIG. 1. In this case, a width d ofthe convex portion may become smaller than designed, which makes itdifficult to obtain desired electrical properties.

Incidentally, when the silicon oxide film to be used as a gate oxidefilm is formed by the CVD method or the ALD method, a boundary betweenthe thin film and the silicon wafer may become less flat, which may leadto defects, compared to where the silicon oxide film is formed by athermal oxidization process. Patent Documents below do not address sucha problem, while describing the ALD method.

Patent Document 1: U.S. Pat. No. 7,153,542.

Patent Document 2: Japanese Patent Publication No. 3,144,664.

Patent Document 3: U.S. Pat. No. 6,869,641.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and isdirected to a technology that can yield a thin film having a sufficientdensity along a thickness direction when the thin film is deposited on asubstrate by repeatedly alternately supplying plural kinds of gases tothe substrate under vacuum. In addition, the present invention providesa technology contributing to fabrication of high-performancesemiconductor devices.

According to a first aspect of the present invention, there is provideda film deposition apparatus that forms a thin film on a substrate byrepeating a cycle of alternately supplying plural kinds of reactiongases to the substrate under vacuum, wherein a first reaction gas amongthe plural kinds of the reaction gases reacts with a second reaction gasamong the plural kinds of the reaction gases, the second reaction gasbeing adsorbed on the substrate, thereby to produce a reaction product.The film deposition apparatus includes a susceptor that is provided in avacuum chamber and includes a substrate receiving area in which asubstrate is placed; an evacuation system that evacuates the vacuumchamber; plural reaction gas supplying parts that supply thecorresponding reaction gases to the substrate placed in the substratereceiving area; a plasma generation part that generates plasma includinga chemical component that reacts with the second reaction gas adsorbedon the substrate, and supplies the plasma to the substrate duringformation of a thin film of the reaction product thereby to alter thethin film on the substrate; and a controlling part that outputs acontrolling signal in order to change plasma intensity of the plasmathat is generated and supplied to the substrate by the plasma generationpart at a predetermined point of time to a different plasma intensitybefore the predetermined point of time.

According to a second aspect of the present invention, there is provideda film deposition method that forms a thin film on a substrate byrepeating a cycle of alternately supplying plural kinds of reactiongases to the substrate under vacuum, wherein a first reaction gas amongthe plural kinds of the reaction gases reacts with a second reaction gasamong the plural kinds of the reaction gases, the second reaction gasbeing adsorbed on the substrate, thereby to produce a reaction product.The film deposition method includes steps of placing a substrate in asubstrate receiving area of a susceptor provided in a vacuum chamber;evacuating the vacuum chamber; alternately supplying plural kinds of thereaction gases to the substrate in the substrate receiving area fromcorresponding reaction gas supplying parts thereby to form a thin filmon the substrate; supplying plasma including a chemical component thatreacts with the second reaction gas adsorbed on the substrate from aplasma generation part to the substrate when the thin film is beingformed, thereby to alter the thin film on the substrate; and changingplasma intensity of the plasma supplied to the substrate, at apredetermined point of time to a different plasma intensity of theplasma that is generated and supplied to the substrate by the plasmageneration part before the predetermined point of time.

According to a third embodiment of the present invention, there isprovided a film deposition method that forms a thin film on a substrateby repeating a cycle of alternately supplying plural kinds of reactiongases to the substrate under vacuum, wherein a first reaction gas amongthe plural kinds of the reaction gases reacts with a second reaction gasamong the plural kinds of the reaction gases, the second reaction gasbeing adsorbed on the substrate, thereby to produce a reaction product.The film deposition method includes steps of placing a substrate in asubstrate receiving area of a susceptor provided in a vacuum chamber;evacuating the vacuum chamber; supplying the plural kinds of thereaction gases from corresponding reaction gas supplying parts towardthe susceptor; supplying plasma including a chemical component thatreacts with one of the second reaction gas adsorbed on the substrate andat least apart of the substrate from the plasma generation part towardthe susceptor; and rotating the susceptor around a vertical axis so thatthe substrate receiving area passes alternately through a supplying areato which the second reaction gas is supplied, a reaction area where thefirst reaction gas reacts with the second reaction gas adsorbed on thesubstrate, and a plasma area that is arranged downstream relative to thereaction area along a rotation direction of the susceptor and where theplasma is supplied, wherein the supplying area, the reaction area, andthe plasma area are arranged at intervals along a circumferentialdirection of the vacuum chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a thin film obtained by aconventional method;

FIG. 2 is a cross-sectional view illustrating a film depositionapparatus according to an embodiment of the present invention, where theview is taken along I-I′ line in FIG. 4;

FIG. 3 is a perspective view illustrating an inner structure of the filmdeposition apparatus;

FIG. 4 is a plan view illustrating the film deposition apparatus;

FIG. 5 is a perspective view illustrating apart of the inner structureof the film deposition apparatus;

FIG. 6 is a cross-sectional view illustrating a part of the innerstructure of the film deposition apparatus;

FIG. 7 is another cross-sectional view illustrating a part of the innerstructure of the film deposition apparatus;

FIG. 8 is a cross-sectional view illustrating an example of an activatedgas injector provided in the film deposition apparatus;

FIG. 9 is a cross-sectional view illustrating a substrate subject to aprocess performed in the film deposition apparatus;

FIG. 10 is a schematic view illustrating a process performed in the filmdeposition apparatus;

FIG. 11 is an explanatory view for explaining plasma intensity;

FIG. 12 is a schematic view illustrating a process flow;

FIG. 13 is another schematic view illustrating a process flow, followingFIG. 12;

FIG. 14 is yet another schematic view illustrating a process flow,following FIG. 13;

FIG. 15 is a schematic view illustrating an alteration step performed inthe film deposition apparatus;

FIG. 16 is a schematic view illustrating gas flow in the film depositionapparatus;

FIG. 17 is a schematic view illustrating a substrate processed in thefilm deposition apparatus;

FIG. 18 is a schematic view illustrating another process performed inthe film deposition apparatus;

FIG. 19 is a schematic view illustrating yet another process performedin the film deposition apparatus;

FIG. 20 is an explanatory view for explaining another example of thepresent invention;

FIG. 21 is a schematic view illustrating a process performed withrespect to a substrate, according to another example of the presentinvention;

FIG. 22 is another schematic view illustrating a process performed withrespect to a substrate, according to another example of the presentinvention;

FIG. 23 is a schematic view illustrating a process performed withrespect to a substrate, according to another example of the presentinvention;

FIG. 24 is a schematic view illustrating a process performed withrespect to a substrate, according to another example of the presentinvention;

FIG. 25 is an explanatory view for explaining a process according toanother example of the present invention;

FIG. 26 is a schematic view illustrating another process according toanother example of the present invention;

FIG. 27 is a schematic view illustrating another process according toanother example of the present invention;

FIG. 28 is a schematic view illustrating another process according toanother example of the present invention;

FIG. 29 is a schematic view illustrating another process according toanother example of the present invention;

FIG. 30 is a cross-sectional view of another film deposition apparatusaccording to another example of the present invention;

FIG. 31 is a graph illustrating a relationship between an oxide filmthickness and an inner pressure in a vacuum chamber of the filmdeposition apparatus;

FIG. 32 is a graph illustrating a relationship between an oxide filmthickness and high frequency power supplied to electrodes thereby togenerate plasma;

FIG. 33 is a graph illustrating a relationship between a film shrinkageand an oxide film thickness; and

FIG. 34 is a graph illustrating a relationship between an increased filmthickness and plasma irradiation time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

According to embodiments of the present invention, a thin film formed ona substrate by repeatedly alternately supplying plural kinds of gases tothe substrate under vacuum can be sufficiently densified along athickness direction, because an alteration step where the substrate isexposed to plasma during the film deposition is carried out. Inaddition, because plasma intensity of the plasma is changed during thefilm deposition, influence incurred on the underlying layer of the thinfilm by the plasma can be controlled, and properties of the thin filmcan be uniform along the thickness direction, thereby contributing tofabrication of high-performance semiconductor devices.

A First Embodiment

A film deposition apparatus according to a first embodiment of thepresent invention is explained referring to FIGS. 1 through 7. The filmdeposition apparatus has a vacuum chamber 1 having a flattened cylindershape, and a turntable 2 that is located inside the chamber 1 and has arotation center at a center of the vacuum chamber 1. The vacuum chamber1 is made so that a ceiling plate 11 can be separated from a chamberbody 12. The ceiling plate 11 is pressed onto the chamber body 12 via asealing member such as an O ring 13, so that the vacuum chamber 1 issealed in an airtight manner. On the other hand, the ceiling plate 11can be raised by a driving mechanism (not shown) when the ceiling plate11 has to be removed from the chamber body 12.

The turntable 2 is attached on a cylindrically shaped core portion 21.The core portion 21 is attached on a top end of a rotational shaft 22that extends in a vertical direction. The rotational shaft 22 goesthrough a bottom portion 14 of the chamber body 12 and is attached atthe lower end to a driving mechanism 23 that can rotate the rotationalshaft 22 clockwise, in this embodiment. The rotational shaft 22 and thedriving mechanism 23 are housed in a case body 20 having a cylinder witha bottom. The case body 20 is attached in an airtight manner to a bottomsurface of the bottom portion 14 via a flange part, which maintainsairtightness of an inner environment of the case body 20 from an outerenvironment.

As shown in FIGS. 2 and 3, plural (five in the illustrated example)circular concave portions 24, each of which receives a substrate wafer W(referred to as a wafer), are formed in an upper surface of theturntable 2. The concave portions 24 are located along a circumferentialdirection (or a rotational direction of the turntable 2). The wafer Whas plural convex parts 90 having pillar or line shapes on the uppersurface of the wafer W, as shown in FIG. 9. Incidentally, only one waferW placed in one of the concave portions 24 is illustrated in FIG. 3.

As shown in FIG. 4, the concave portion 24 has a diameter slightlylarger, for example, by 4 mm than the diameter of the wafer W and adepth equal to a thickness of the wafer W. Therefore, when the wafer Wis placed in the concave portion 24, a surface of the wafer W is at thesame elevation of a surface of an area of the turntable 2, the areaexcluding the concave portions 24. The concave portions 24 are wafer Wreceiving areas provided to position the wafers W and prevent the wafersW from being thrown out by centrifugal force caused by rotation of theturntable 2. In the bottom of the concave portion 24 there are formedthree through-holes (not shown) through which three correspondingelevation pins (described later) are raised/lowered. The elevation pinssupport a back surface of the wafer W and raise/lower the wafer W.

As shown in FIGS. 3 and 4, a first reaction gas nozzle 31, a secondreaction gas nozzle 32, separation gas nozzles 41, 42, and an activatedgas injector 220, all of which may be formed of, for example, quartz,are arranged in radial directions and at predetermined angular intervalsin the circumferential direction (or the rotation direction of theturntable 2). The nozzles 31, 32, 41, 42 oppose an area through whichthe concave portions 24 of the turntable 2 pass. In the illustratedexample, the activated gas injector 220, the separation gas nozzle 41,the first reaction gas nozzle 31, the separation gas nozzle 42, and thesecond reaction gas nozzle 31 are arranged in this order in a clockwisedirection (or the rotation direction of the turntable 2) from a transferopening 15 (described later). The activated gas injector 220 and thenozzles 31, 32, 41, 42 are introduced into the vacuum chamber 1 from anouter circumferential wall of the chamber body 12, in order to extendalong a radius direction of the chamber body 12 and to be parallel withthe upper surface of the turntable 2. Gas introduction ports 31 a, 32 a,41 a, 42 a serving as base ends of the corresponding nozzles 31, 32, 41,42 go through the outer circumferential wall of the chamber body 12. Thefirst reaction gas nozzle 31 and the second reaction gas nozzle 32 serveas a first reaction gas supplying portion and a second reaction gassupplying portion, respectively; and the separation gas nozzles 41, 42serve as a separation gas supplying portion. The activated gas injector220 is described later.

The reaction gas nozzle 31 is connected to a gas supplying source (notshown) of a first reaction gas containing silicon (Si) such as adiisopropyl amino silane (DIPAS) gas and a bis (tertiary-butylamino)silane (SiH₂ (NH—C (CH₃)₃)₂: BTBAS) gas, via a flow rate control valve(not shown). The second reaction gas nozzle 32 is connected to a gassupplying source (not shown) of a second reaction gas such as a mixedgas of ozone (O₃) gas and oxygen (O₂) gas, or the combination thereof,via a flow rate control valve (not shown). The separation gas nozzles41, 42 are connected to a gas supplying source (not shown) of nitrogen(N₂) gas serving as a separation gas, via a flow rate control valve (notshown). Incidentally, the following explanation is made with the O₃ gasused as the second reaction gas.

The reaction gas nozzles 31, 32 have plural ejection holes (not shown)open downward arranged in longitudinal directions of the reaction gasnozzles 31, 32, for example, at equal intervals thereby to eject thecorresponding source gases to the turntable 2. An area below thereaction gas nozzle 31 is a first process area P1 in which thesilicon-containing gas is adsorbed on the wafer W. An area below thesecond reaction gas nozzle 32 is a second process area P2 in which thesilicon-containing gas adsorbed on the wafer W is oxidized by the O₃gas.

The separation gas nozzles 41, 42 have plural ejection holes (not shown)arranged, for example, at equal intervals in longitudinal directions ofthe separation gas nozzles 41, 42 thereby to eject the separation gasesdownward from the plural ejection holes 40. The separation nozzles 41,42 form corresponding separation areas D that separate the first processarea P1 and the second process area P2. In the separation area D, aconvex portion 4 having a top view shape of a sector is provided on thelower surface of the ceiling plate 11 of the vacuum chamber 1, as shownin FIGS. 3 and 4. The separation gas nozzles 41, 42 are housed in grooveportions (not shown) in the corresponding convex portions 4.

With the above configuration, there are flat low ceiling surfaces 44(first ceiling surfaces) on both sides of the separation gas nozzle 41(or 42), and high ceiling surfaces 45 (second ceiling surfaces) outsideof the corresponding low ceiling surfaces 44. Taking for an example theseparation area D where the separation gas nozzle 41 is provided, thisseparation area D impedes the second reaction gas, which flows in therotation direction of the turntable 2, from entering a space below theconvex portion 4, and the first reaction gas, which flows in a directionopposite to the rotation direction of the turntable 2, from entering thespace below the convex portion 4.

On the other hand, a protrusion portion 5 is provided on the lowersurface of the ceiling plate 11, as shown in FIGS. 6 and 7. Theprotrusion portion 5 is formed to be continuous with the inner arc ofthe convex portion 4, in this embodiment, so that the lower surface ofthe protrusion portion 5 is at the same level as that of the convexportion 4 (or the ceiling surface 44). FIGS. 3 and 4 illustrate thevacuum chamber 1 as if the vacuum chamber 1 was horizontally severed ata level lower than the ceiling surface 45 and higher than the separationnozzles 41, 42. In addition, FIG. 2 illustrates a vertical cross sectionof the vacuum chamber 1 where the high ceiling surfaces 45 are provided,and FIG. 6 illustrates half of a vertical cross section of the vacuumchamber 1 where the low ceiling surface 44 is provided.

In a circumferential portion of the sector-shaped convex portion 4 (oran outer circumferential portion facing the inner surface of the chamberbody 12), there is provided a bent portion 46 that bends in an L-shape,as shown in FIGS. 3 and 6. The bent portion 46 opposes the outercircumferential surface of the turntable 2 with a slight gap in relationto the inner circumferential surface of the chamber body 12. The bentportion 46 is provided in order to impede the reaction gases fromentering the separation area D from the both sides of the separationarea D and from being mixed. Gaps between the outer circumferentialsurface of the turntable 2 and the inner circumferential surface of thebent portion 46 and between the outer circumferential surface of thebent portion 46 and the inner circumferential surface of the chamberbody 12 may be as narrow as the height of the ceiling surface 44 withrespect to the turntable 2, for example.

A circumferential wall of the chamber body 12 is indented outward inareas that do not correspond to the separation areas D, as shown inFIGS. 2 and 4, so that there is a relatively large space with respect tothe outer circumferential surface of the turntable 2 and from the bottomof the chamber body 12 up to the outer circumferential surface of theturntable 2. In the following explanation, the space havingsubstantially a box shape is referred to as an evacuation area.Specifically, the evacuation area in gaseous communication with thefirst process area P1 is referred to as a first evacuation area E1, andthe evacuation area in gaseous communication with the second processarea P2 is referred to a second evacuation area E2, hereinafter (seeFIG. 4). At the bottoms of the first and the second evacuation areas E1,E2, a first evacuation port 61 and a second evacuation port 62 areformed, respectively, as shown in FIGS. 2 and 4. The first and thesecond evacuation ports 61, 62 are connected to a vacuum pump 64 servingas an evacuation unit via an evacuation pipe 63, as shown in FIG. 2. Theevacuation pipe 63 is provided with a pressure controller 65 thatcontrols an inner pressure in the vacuum chamber 1.

As shown in FIGS. 2 and 6, a heater unit 7 serving as a heating portionis provided in a space between the bottom portion 14 of the chamber body12 and the turntable 2, so that the wafers W placed on the turntable 2can be heated through the turntable 2 at a predetermined temperature,for example 300° C., which is determined by a process recipe. Inaddition, a ring-shaped cover member 71 is provided beneath theturntable 2 and near the outer circumference of the turntable 2 in orderto surround the heater unit 7, so that the space where the heater unit 7is placed is partitioned from the outside area of the cover member 71,thereby impeding the gas from entering the space below the turntable 2.The cover member 71 includes an inner member 71 a provided to face theouter circumferential portion of the turntable 2 and an area outside ofthe turntable 2 from below, and an outer member 71 b provided betweenthe inner member 71 a and the inner circumferential surface of thechamber body 12, as shown in FIG. 6. The outer member 71 b is severed inpart in order to leave spaces above the evacuation ports 61, 62, therebyallowing a space above the turntable 2 to be in gaseous communicationwith the evacuation ports 61, 62. In addition, the upper surface of theouter member 71 b comes close to the bent portion 46.

Referring to FIG. 2, a part of the bottom portion 14 of the vacuumchamber 1 comes close to the lower surface of the core portion 21. Thispart is referred to as a protrusion portion 12 a. There is a narrowspace between the protrusion portion 12 a and the core portion 21, andthe case body 20 is provided with a purge gas supplying pipe 72. Inaddition, plural purge gas supplying pipes 73 are arranged along thecircumferential direction of the chamber body 12 and connected to areasbelow the heater unit 7 in order to purge the space where the heaterunit 7 is housed. A cover member 7 a, which may be formed of, forexample, quartz glass, is supported by the upper surface of the covermember 71 and the upper portion of the protrusion portion 12 a, so thatthe heater unit 7 is covered by the cover member 7 a and thus gases aresubstantially impeded from entering the space where the heater unit 7 ishoused.

In addition, a separation gas supplying pipe 51 is connected to the topcenter portion of the ceiling plate 11 of the vacuum chamber 1, so thatN₂ gas is supplied as a separation gas to a space 52 between the ceilingplate 11 and the core portion 21. The separation gas supplied to thespace 52 flows through a narrow gap 50 between the protrusion portion 5and the turntable 2 and then along the top surface of the turntable 2 tothe outer circumference of the turntable 2, thereby impeding thereaction gases (silicon-containing gas and O₃ gas) from being intermixedthrough the center portion of the turntable 2. Incidentally, an areadefined by the ceiling plate 11, the core portion 21, and the protrusionportion 5 is referred to as a center area C.

Moreover, the vacuum chamber 1 is provided in the outer circumferentialwall with the transport opening 15 through which the wafer W istransferred into or out from the vacuum chamber 1 by a transfer arm 10(see FIG. 3). The transfer opening 15 is provided with a gate valve (notshown) by which the transfer opening 15 is opened or closed. Because thewafer W is transferred into the vacuum chamber 1 through the transferopening 15 and placed in the concave portion 24 in the turntable 2, liftpins are provided in an area facing the transfer opening 16 below theturntable 2. The lift pins can be moved upward/downward throughcorresponding through-holes (not shown) formed in the turntable 24 by anelevation mechanism (not shown), so that the wafer W is transferredbetween the transfer arm 10 and the concave portion 24 of the turntable2.

Next, the activated gas injector 220 is described. The activated gasinjector 220 is arranged to generate plasma in an area above the concaveportions 24 of the turntable 2 and along the radius direction of theturntable 2 thereby to alter properties of a silicon oxide filmdeposited on the wafers W through reaction of the silicon-containing gasand the O₃ gas. As shown in FIGS. 5 and 8, the activated gas injector220 is provided with a gas introduction nozzle 34 that may be made of,for example, quartz glass and serves as a property alteration gassupplying portion that supplies a process gas from which plasma issubstantially generated in the vacuum chamber 1, and a pair of sheathpipes 35 a, 35 b located downstream relative to the gas introductionnozzle 34 along the rotation direction of the turntable 2. The sheathpipes 35 a, 35 b extend parallel with each other and generate the plasmafrom the process gas supplied from the gas introduction nozzle 34. Inaddition, the gas introduction nozzle 34 and the sheath pipes 35 a, 35 bare introduced in an air-tight manner from the outer circumferentialwall of the chamber body 12 to the center of the turntable 2, areparallel with the wafer W on the turntable 2, and orthogonally traversethe rotation direction of the turntable 2. Protection pipes 37 areconnected to a base end side of the sheath pipes 35 a, 35 b (FIGS. 3 and8). Plural gas holes 341 are formed in and along a longitudinaldirection of the gas introduction nozzle 34.

Referring to FIG. 4, the gas introduction nozzle 34 is connected to oneend of a plasma gas introduction line 251 that supplies the process gasfor generating the plasma, and the other end of the plasma gasintroduction line 251 is branched into two branch lines that areconnected to an argon (Ar) gas supplying source 254 and an oxygen (O₂)gas supplying source 255, respectively. Each of the two branch lines isprovided with a valve 252 and a flow rate controller 253.

The sheath pipes 35 a, 35 b may be made of, for example, quartz, alumina(aluminum oxide), ittria (ittrium oxide), or the like. As shown in FIG.8, electrodes 36 a, 36 b are inserted into the corresponding sheathpipes 35 a, 35 b thereby to constitute parallel electrodes. Theelectrodes 36 a, 36 b may be made of, for example, nickel alloy,titanium, or the like. A distance k between the electrodes 36 a, 36 band the wafer W on the turntable 2 is about 7 mm in this embodiment.These electrodes 36 a, 36 b are connected to a high frequency powersupply 224 via a matching box 225, as shown in FIG. 4. High frequencyelectric power, which may have, for example, a frequency of 13.56 MHzand electric power of 500 W or less, is supplied to the electrodes 36 a,36 b from the high frequency power supply 224. Incidentally, the sheathpipes 35 a, 35 b are simplified in the drawings except for FIG. 8.

As shown in FIG. 8, the gas introduction nozzle 34 and the sheath pipes35 a, 35 b are provided with a cover body 221. The cover body 221 isarranged to cover a top and side (both sides along the long and shortedges) of the gas introduction nozzle 34 and the sheath pipes 35 a, 35b. The cover body 221 is made of an insulating material such as quartz.In addition, the cover body 221 is provided with flow limiting surfaces222 that extend in a flange shape. Specifically, the flow limitingsurfaces 222 are provided from one end through the other end of thecover body 221 along the longitudinal direction of the cover body 221and extend outward from the corresponding lower edge portions of thecover body 221. According to the flow limiting surfaces 222, the gasessuch as the O₃ gas and the N₂ gas flowing along the rotation directionof the turntable 2 over the upper surface of the turntable 2 are impededfrom entering the inside of the cover body 221. In addition, the flowlimiting surfaces 222 are arranged close to the upper surface of theturntable 2 so that a gap t between the flow limiting surface 222 andthe upper surface of the turntable 2 is small enough to efficientlyimpede the gases from entering the inside of the cover body 221.Moreover, the flow limiting surface 222 has a width u that becomesgreater in the rotation direction of the turntable 2 along a directiontoward the inner circumferential surface of the chamber body 12. Thecover body 221 is supported by plural supporting members 223 (see FIG.6) connected to the ceiling plate 11 of the vacuum chamber 1.

In addition, the film deposition apparatus according to this embodimentis provided with a controlling part 100, which is made of a computer,for controlling entire operations of the film deposition apparatus. Thecontrolling part 100 includes a memory device (not shown) that stores acomputer program that causes the film deposition apparatus to carry outa film deposition—alteration step including a film deposition step andan alteration step. Here, the film deposition step and the alterationstep are briefly explained. In the film deposition step, the siliconoxide film, which is made of the reaction product of thesilicon-containing gas and the O₃ gas, is formed, and in the alterationstep, the reaction product is altered or densified. In addition, thefilm deposition step and the alteration step are alternately repeated sothat plural layers of the reaction product are accumulated on the waferW. In this case, the controlling part 100 outputs a controlling signalto the high frequency power source 224 in order to adjust (or change)plasma intensity in the alteration step so that the silicon oxide filmis uniformly altered in a thickness direction of the silicon oxide filmwhile the plasma is prevented from penetrating through the silicon oxidefilm to reach the wafer W, which is made of silicon. For example, when afilm thickness of the silicon oxide is small, or at an initial stage ofthe repeatedly performed film deposition and alteration step, the plasmaintensity is zero, and as the film thickness is increased, or as thenumber of the film deposition steps is increased, the plasma intensityis increased in a stepwise manner, as shown in FIG. 10. Incidentally,the controlling portion 100 may output a controlling signal to thepressure controller 65 in order to adjust the inner pressure in thevacuum chamber 1.

Here, “plasma intensity” is referred to as intensity of plasma to whichthe wafer W is exposed, and differs depending on electric power suppliedto the electrodes 36 a, 36 b, an inner pressure in the vacuum chamber 1,an exposure time of the plasma to the wafer W, a distance k between theelectrodes 36 a, 36 b, and the like. In order to quantitatively expressthe “plasma intensity”, a film thickness j of a silicon oxide filmobtained by continuously exposing the upper surface of the wafer W (or asilicon layer) to plasma for 180 s, as shown in FIG. 10, is used as anindicator in this embodiment. For example, when a silicon oxide filmhaving a thickness of 1 nm is obtained after the upper surface of thewafer W is exposed to plasma for 180 s under certain conditions, theplasma intensity in this case is expressed as “plasma intensitycorresponding to the film thickness j of 1 nm”. Similarly, when asilicon oxide film having a thickness of 2 nm is obtained, the plasmaintensity is expressed as “plasma intensity corresponding to the filmthickness j of 2 nm”.

When the film deposition—alteration process is being carried out, theplasma intensity is adjusted with electric power supplied to theelectrodes 36 a, 36 b while other parameters such as the inner pressurein the vacuum chamber 1 are kept constant. Specifically, when thedistance k between the electrodes 36 a, 36 b and the wafers W havingdiameters of 300 mm is set to the above value and the inner pressure inthe vacuum chamber 1 is kept at 266 Pa (2 Torr), the electric powersupplied to the electrodes 36 a, 36 b of 30 W provides the filmthickness j corresponding to 1 nm, and the electric power supplied tothe electrodes 36 a, 36 b of 65 W provides the film thickness jcorresponding to 2 nm. A relationship between the electric power and thefilm thickness j depends on process conditions, and thus preferably isobtained in advance by, for example, carrying out an experiment using,for example, test wafers, under predetermined conditions.

Incidentally, the program includes groups of steps or instructions thatcause the constituting members or parts of the film deposition apparatusto perform the film deposition—alteration process. The program is storedin a memory portion 101 (FIG. 4), which is a computer readable storagemedium such as a hard disk, a compact disk, a magneto-optical disk, amemory card, a flexible disk, or the like, and installed into thecontrol part 100.

Next, the operations of the film deposition apparatus according to thisembodiment (film deposition method) are described in the following.First, the wafer W is transferred into the vacuum chamber 1 through thetransfer opening 15 by the transferring arm 10, after the gate valve(not shown) is opened. Specifically, when one of the concave portions 24of the turntable 2 is in alignment with the transfer opening 15 byappropriately rotating the turntable 2, the wafer W is placed in theconcave portion 24 of the turntable 2 by the lift pins (not shown) andthe transfer arm 10 that cooperatively operate. Such operations areintermittently repeated so that five wafers W are placed in thecorresponding concave portions 24 of the turntable 2. Next, after thetransfer arm 10 recedes from the vacuum chamber 1, the gate valve (notshown) is closed, and the vacuum chamber 1 is evacuated to the lowestreachable pressure by the vacuum pump 64. Then, the turntable 2 startsrotating in a clockwise direction at a rotational speed of, for example,120 revolutions per minute, and the wafers W on the turntable are heatedat, for example, 300° C. The N₂ gas is supplied at predetermined flowrates from the separation gas nozzles 41, 42, the separation gassupplying pipe 51, and the purge gas supplying pipes 72. Subsequently,the silicon-containing gas is supplied from the reaction gas nozzle 31;the O₃ gas is supplied from the second reaction gas nozzle 32; and theAr gas and the O₂ gas are supplied at flow rates of, for example, 9.5standard liters per minute (slm) and 0.5 slm, respectively, from the gasintroduction nozzle 34. The vacuum chamber 1 is maintained at apredetermined pressure, for example, 266 Pa (2 Torr) by the pressurecontroller 65.

With the rotation of the turntable 2, the silicon-containing gas isadsorbed on the upper surface of the wafer W in the first process areaP1, and the adsorbed silicon-containing gas on the upper surface of thewafer W is oxidized by the O₃ gas in the second process area P2, so thatone molecular layer or plural molecular layers of the reaction product,i.e., silicon oxide is formed in the film deposition step (or a cycle ofsupplying reaction gases to the upper surface of the wafer W). In thiscase, because no high frequency power is supplied to the electrodes 36a, 36 b, the plasma intensity is zero (a first plasma intensity). Withthis, the molecular layer or the plural molecular layers may includeimpurities such as organic groups and/or moisture (OH groups), whichoriginate from, for example, the silicon-containing gas. After the filmdeposition step is continued by rotating the turntable 2 until a filmthickness of the silicon oxide film becomes 1 nm, as shown in FIGS. 10and 12, high frequency power of 45 W (a second plasma intensity) isapplied across the electrodes 36 a, 36 b so that the plasma intensitycorresponds to the oxide film thickness j of 1.5 nm. Incidentally, FIG.12 schematically illustrates the wafer W and the reaction productdeposited on the wafer W. FIGS. 13 and 14, which are referred to later,also schematically illustrate the wafer W and the reaction product.

In the activated gas injector 220, the Ar gas ejected from the gasintroduction nozzle 34 toward the sheath pipes 35 a, 35 b is activatedby high frequency electric power between the sheath pipes 35 a, 35 binto plasma including ions and/or radicals, which in turn flow downwardtoward the wafers W on the turntable 2, which is rotated, below theactivated gas injector 220. When the wafer W reaches the area below theactivated gas injector 220, the wafer W is exposed to the plasma andthus the alteration step that alters the silicon oxide film is carriedout. Specifically, because the wafer W is bombarded with, for example,the ions and/or radicals, the impurities are degassed from the siliconoxide film, and the silicon atoms and the oxygen atoms are rearranged,resulting in densification of the silicon oxide film, as schematicallyshown in FIG. 15.

In this case, because the plasma intensity is set as described above,the plasma can enter or penetrate the silicon oxide film from the uppersurface thereof through a vicinity of the upper surface of theunderlying substance, which is the wafer W (silicon) in the illustratedexample, as shown on the left side view of FIG. 13. Therefore, thesilicon oxide film formed at the plasma intensity of zero (see the rightside view of FIG. 12) can be uniformly altered in the thicknessdirection by the penetrating plasma, while the upper surface of thewafer W (silicon) is prevented from being oxidized. This filmdeposition—alteration step including the film deposition step and thealteration step is repeated plural times by rotating the turntable 2until a film thickness of the silicon oxide film becomes 2 nm. Withthis, a thickness of the silicon oxide film is increased, and thus thelowest level (or the depth from the upper surface of the silicon oxidefilm) that the plasma can reach becomes gradually moved away from theupper surface of the wafer W. Incidentally, arrows in FIG. 13schematically illustrate the plasma intensity. Arrows in FIG. 14, whichis referred to later, also illustrate the plasma intensity.

Because the separation area D is not provided between the activated gasinjector 220 and the second reaction gas injector 32 in the vacuumchamber 1, the O₃ gas and the separation gas (N₂ gas) flow toward theactivated gas injector 220 from the upstream side of the activated gasinjector 220 because of rotation of the turntable 2. However, such gasesare least likely to flow through the space between the activated gasinjector 220 and the turntable 2, because the gases flow through abovethe activated gas injector 220. This is because the activated gasinjector 220 is provided with the cover body 221. Incidentally, theimpurities removed from the silicon oxide film during the alterationstep are turned into gas, and then the gas is evacuated together withthe O₂ gas and the N₂ gas.

In addition, because the N₂ gas is supplied between the first processarea P1 and the second process area P2 and the N₂ gas is supplied to thecenter area C, the silicon-containing gas and the O₃ gas are notintermixed with each other and are evacuated to the correspondingevacuation ports 61, 62. Incidentally, because the area below theturntable 2 is purged with the N₂ gas, for example, thesilicon-containing gas that has flowed into the evacuation area E1 (orE2) cannot flow into the area where the O₃ gas is supplied through thespace below the turntable 2.

Then, high frequency power is applied, for example, at 150 W across theelectrodes 36 a, 36 b in order to obtain the plasma intensitycorresponding to the oxide film thickness j of 3.7 nm. In this case, theplasma can only reach the vicinity of the upper surface of the wafer W,as shown in FIG. 14, so that the silicon oxide film deposited on thewafer W is uniformly altered, but the upper surface of the wafer W isprevented from being oxidized. Next, the film deposition—alteration stepis continued until a thickness of the silicon oxide film becomes 10 nm,a silicon oxide film, which has been densified along the film thicknessdirection, is formed to cover the convex portions 90 formed on the uppersurface of the wafer W, while the upper surface of the wafer W isprevented from being oxidized, as shown in FIG. 17. Therefore, reductionof the width d of the convex portion 90, which may be caused by siliconoxide grow due to irradiation of plasma, can be avoided.

According to this embodiment, when the film deposition—alterationprocess composed of the film deposition step, where the reaction productis formed on the wafer W using the silicon-containing gas and the O₃gas, and the alteration step, where the reaction product is altered byplasma, is repeated plural times, the plasma intensity is set to zerowhen a thickness of the reaction product (or at an initial stage of thefilm deposition—alteration process), and then the plasma intensity ofthe plasma supplied to the wafer W is increased in a stepwise manner asa thickness of the reaction product is increased (or as the number ofthe film deposition steps is increased). Therefore, the thin film, whichis densified along the thickness direction uniformity, can be obtainedwhile the upper surface of the wafer W can be prevented from beingoxidized, thereby yielding an excellent device structure with a desiredfeature as shown in FIG. 17.

In addition, in the film deposition—alteration process, the alterationstep is carried out with respect to the wafer W when the wafer W movesalong from the second process area P2 to the first process area P1 inthe vacuum chamber 1 every time after the film deposition step, in sucha manner that the film deposition is not influenced by the alterationstep. In addition, because the alteration process is carried out everytime after the film deposition step in the film deposition—alterationprocess, the thin film can be altered in a shorter time compared to acase where the thin film is altered after the film deposition iscompleted.

Incidentally, while the plasma intensity is increased in a stepwisemanner in the above example, the plasma intensity is continuouslyincreased as the number of the film deposition steps is increased, orevery turn of the turntable 2, as shown in FIGS. 18 and 19. Also in thiscase, the plasma intensity is set to zero at an initial stage of thefilm deposition—alteration process, or until a thickness of the reactionprocess reaches, for example, 1 nm. By adjusting the plasma intensity,the plasma can reach the vicinity of the upper surface of the wafer W,which underlies the thin film of the reaction product, in the alterationstep. Therefore, the film can be uniformly altered along the thicknessdirection. Incidentally, FIG. 19 schematically illustrates the wafer Wand the reaction product on the wafer W, where the plasma intensity isschematically represented by arrows.

Here, at the initial stage of the film deposition—alteration process,the high frequency power may be supplied at 5 W to the electrodes 36 a,36 b so that the plasma intensity corresponds to the oxide filmthickness j of 0.2 nm. However, the plasma intensity is preferably setto zero because it is not easy to maintain the plasma at such a lowerlevel.

A Second Embodiment

Next, a second embodiment of the present invention is explained, where asilicon oxide film serving as a gate electrode film is formed on asubstrate. While it is especially important for the gate electrode filmto have excellent flatness at a boundary between the silicon oxide filmand the underlying silicon wafer, a silicon oxide film formed by aconventional Chemical Vapor Deposition (CVD) method, an Atomic LayerDeposition (ALD) method or a Molecular Layer Deposition (MLD) method mayhave relatively degraded flatness, as schematically illustrated in FIG.20, compared to a thermally grown silicon oxide film. In the following,a film deposition method according to the second embodiment of thepresent invention, which can form a silicon oxide film having excellentflatness at a boundary between the silicon oxide film and the underlyingsilicon wafer.

Specifically, when the film deposition step and the alteration step arealternately performed by rotating the turntable 2, the alteration stepis performed at a second plasma intensity, which corresponds to theoxide film thickness j of 5.3 nm (or by setting the high frequency powersupplied to the electrodes 36 a, 36 b to 400 W) until a thickness of thereaction product reaches 3 nm, as shown in FIG. 24. This plasma canreach the wafer W through the thin film of the reaction product, therebyoxidizing the upper surface (or portion) of the wafer W, as shown inFIG. 21.

Therefore, a first silicon oxide film 92 that is formed through theoxidization of the wafer W and a second silicon oxide film 93 that isformed by the film deposition—alteration process are formed on anunderlying layer 91, which corresponds to an upper portion of the waferW, as shown in FIG. 22. Namely, a silicon oxide film 94 composed of thefirst silicon oxide film 92 and the second silicon oxide film 93 isformed on the wafer W (the underlying film 91). Because theplasma-oxidized first silicon oxide film is generally likely to providebetter flatness at the boundary in relation to the underlying film thanthe thermally grown silicon oxide film, an excellent flatness can beachieved between the silicon oxide film 94 and the underlying film 91.

Then, the film deposition step and the alteration step, which isperformed at a first plasma intensity corresponding to the oxide filmthickness j of 3.7 nm, are alternately performed until a thickness ofthe reaction product reaches 10 nm. With this, a thin film that isdensified along the thickness direction and provides excellent flatnessat the boundary in relation to the underlying film 91 can be obtained.Here, the plasma intensity is reduced from that corresponding to theoxide film thickness j of 5.3 nm to that corresponding to the oxide filmthickness j of 3.7 nm, in order to avoid a further increase of athickness of the first silicon oxide film 92 and to desirably control athickness of the silicon oxide film 94.

Incidentally, while the plasma intensity is set to be relatively largeat the initial stage of the film deposition in order to oxidize theupper surface (or portion) of the wafer W to form the plasma-oxidizedsilicon oxide film 92 in this embodiment, the plasma-oxidized siliconoxide film may be formed in the following manner in other embodiments.

Namely, after the wafers W are placed in the substrate receiving areas24 of the turntable 2, the vacuum chamber 1 is maintained at apredetermined pressure with the N₂ gas supplied from the separation gassupplying portions 41, 42 and the like and the turntable 2 startsrotating. Then, the plasma is generated by the activated gas injector220. In this case, because the upper surface of the wafer W is exposedto the plasma, the upper surface is readily oxidized, so that theplasma-oxidized silicon oxide film is obtained. Next, after theturntable 2 is rotated plural (or at least two) times, thesilicon-containing gas, the oxidizing gas, and the separation gases aresupplied to the vacuum chamber 1 from the corresponding gas supplyingnozzles 31, 32, 41, and 42, so that the film deposition step and thealteration step are alternately repeated. Even in this case, thedensified silicon oxide film 94 can be formed on the wafer W. In thiscase, the plasma intensity may be lower after the film deposition stepstarts than before it starts, or may be the same after and before thefilm deposition step starts.

In the first and the second embodiments, influence incurred on theunderlying layer of the thin film by the plasma can be controlled byadjusting the plasma intensity.

A Third Embodiment

Next, a third embodiment of the present invention is explained. FIG. 25schematically illustrates multilayers of the reaction product and theplasma irradiated to the reaction product. Specifically, the plasmairradiated to the reaction product is indicated by arrows in thedrawing, while a thickness of the reaction product is increased. Morespecifically, a vertical length (or range) of each of the arrowsindicates a thickness of the reaction product that is exposed to theplasma as the thickness is increased. In other words, the leftmost arrowindicates that the plasma can penetrate through the reaction producthaving a thickness of about 3 nm into the wafer W from the upper surfaceof the reaction product.

When paying attention to a particular layer of the reaction producthaving a thickness of 3 nm to 10 nm, if the layer is close to the uppersurface of the wafer W, the layer is exposed to the plasma certain timesas long as the plasma can penetrate through the layer, because thealteration step is repeated. However, if the layer is close to the uppersurface of the reaction product having a thickness of 10 nm, the layeris exposed to the plasma fewer times. Namely, the reaction product goesthrough the plasma alteration step different times depending on athickness of the reaction product. On the other hand, when the plasmaintensity is set to the oxide film thickness j of 5.3 nm with respect tothe reaction product having a thickness of 3 nm or less, and is set tothe oxide film thickness j of less than 5.3 nm with respect to thereaction product having a thickness of 3 nm through 10 nm, anirradiation amount of the plasma irradiated to the layer near the uppersurface of the wafer W becomes larger than that irradiated to the layernear the upper surface of the reaction product having a thickness of 10nm.

In view of the above, the plasma intensity is adjusted in thisembodiment so that the irradiation amount of the plasma irradiated tothe reaction product is equalized irrespective of a thickness of thereaction product. Specifically, as shown in FIGS. 26 and 27, an upperportion of the reaction product, which may correspond to thicknesses of8 nm to 10 nm, is exposed to the plasma having a third plasma intensitycorresponding to the oxide film thickness j of 5.3 nm. The third plasmaintensity is greater than that of the plasma irradiated to the reactionproduct having a thickness of 8 nm to 10 nm in the second embodiment(see FIG. 24). In addition, the plasma intensity is set to the oxidefilm thickness j of 1.5 nm in order to reduce the irradiation amount ofthe plasma irradiated to the reaction product having a thickness of 3 nmor less, and linearly increased to the oxide film thickness j of 3.7 nmas a thickness of the reaction product is increased from 3 nm to 8 nm.By adjusting the plasma intensity in such a manner, a degree ofalteration is equalized along the thickness direction of the reactionproduct, and thus a thin film having uniform film properties can beobtained.

In addition, the plasma intensity is set to the oxide film thickness jof 5.3 nm with respect to the reaction product until a thickness of thereaction product reaches 1 nm in order to oxidize the underlying film 91into the silicon oxide film 92, and gradually increased to the oxidefilm thickness j of 5.3 nm as a thickness of the reaction product isincreased from 1 nm to 10 nm, as shown in FIG. 24.

Moreover, properties of the reaction product can be equalized along thethickness direction of the reaction product even in the firstembodiment, in the same manner as the third embodiment. Specifically,the plasma intensity is gradually increased from the oxide filmthickness j of 1.5 nm to the oxide film thickness j of 2 nm as athickness of the reaction product is increased from zero to 4 nm, andthe plasma intensity is set to zero when a thickness of the reactionproduct is from 4 nm to 7 nm. Then, the plasma intensity is graduallyincreased from the oxide film thickness j of 3 nm (or the high frequencypower of 110 W supplied to the electrodes 36 a, 36 b) to the oxide filmthickness j of 5.3 nm as a thickness of the reaction product isincreased from 7 nm to 10 nm. By adjusting the plasma intensity in sucha manner, a thin film having uniform film properties along the thicknessdirection can be obtained while the oxidization of the wafer Wunderneath the thin film (reaction product) is reduced. Even in thiscase, the plasma intensity may be set to zero at the initial stage ofthe film deposition step (or until a thickness of the reaction productbecomes, for example, 1 nm).

As stated above, according to embodiments of the present invention, theplasma intensity may be adjusted as a thickness of the reaction productis increased, depending on desired properties of semiconductor devices.The adjustment of the plasma intensity may be made in order to make theproperties of the thin film of the reaction product uniform ornon-uniform along the thickness direction. For example, when the siliconoxide film is used as a gate oxide film, the flat boundary between theunderlying film 91 and the silicon oxide film 94 can be obtained, sothat carrier mobility in a channel of a field effect transistor can beincreased. In addition, the first silicon oxide film 92 and the secondsilicon oxide film 93 of the silicon oxide film 94 (FIG. 22) can becomelow leakage, high reliability films by exposing the oxide films 92, 93to the plasma having the plasma intensity sufficient to appropriatelyalter the oxide films 92, 93. Moreover, the upper silicon oxide film 93of the silicon oxide film 94 may have a high density and a high gasbarrier characteristic by increasing the plasma intensity. In such ways,the film properties along the thickness direction can be arbitrarilyadjusted.

In the above embodiments, the film deposition step and the alterationstep are alternately performed. Namely, supplying the silicon-containinggas and the O₃ gas and irradiating the plasma to the wafer W areperformed while the turntable 2 is rotated. However, the alteration stepmay be performed every plural film deposition step. In this case, thehigh frequency power is not supplied to the electrodes 36 a, 36 b whenthe film deposition step is performed plural times, but supplied to theelectrodes 36 a, 36 b only when the alteration step is performed. Inaddition, when the alteration step is performed, the silicon-containinggas and the O₃ gas are not supplied to the corresponding process areasP1, P2 (FIG. 3). In this case, the alteration step can be continuouslyperformed plural times by rotating the turntable 2.

While the two parallel electrodes 36 a, 36 b are used in order togenerate the plasma (so-called Capacitively Coupled Plasma (CCP)) in theabove embodiments, a U-shaped electrode may be used. In this case, it ispreferable when a curved portion of the U-shaped electrode is arrangednear the center of the vacuum chamber 1 and two straight portionsseparately go through the outer circumferential wall of the chamber body12 in an airtight manner. When high frequency power is supplied to theU-shaped electrode, so-called Inductively Coupled Plasma (ICP) isgenerated in the vacuum chamber 1. In addition, not only CCP and ICP butalso Surface Wave Plasma (SWP) using microwaves and Electron CyclotronResonance (ECR) Plasma may be employed.

Moreover, the oxidizing gas may be supplied to the wafer W on which thesilicon-containing gas is adsorbed, through the activated gas injector220 rather than the second reaction gas nozzle 32. In this case, aprocess gas (Ar gas and O₂ gas) is supplied to and activated by theactivated gas injector 220, so that the silicon-containing gas adsorbedon the wafer W is oxidized and so-formed silicon oxide is altered by theprocess gas from the activated gas injector 220.

Furthermore, while the high frequency power is adjusted in order tochange the plasma intensity in the above embodiments, the inner pressurein the vacuum chamber 1 may be adjusted instead of or in addition to thehigh frequency power, as explained later. Additionally, O₂ gas or O₃ gasmay be used as the oxidizing gas supplied from the second reaction gasnozzle 32, and Ar gas and O₃ gas may be used as a process gas forgenerating the plasma.

In addition, while the silicon-containing gas and the O₃ gas are used toform the silicon oxide film in the above embodiments, thesilicon-containing gas and ammonia (NH₃) gas may be used as the firstreaction gas and the second reaction gas, respectively, thereby forminga silicon nitride film. In this case, a mixed gas of Ar and ammonia or amixed gas of Ar and nitrogen may be used as a process gas from which theplasma is generated. The film deposition step and the alteration stepare alternately performed using these gases. Namely, when the plasmaintensity is reduced or set to zero at the initial stage of the filmdeposition step and then increased as a thickness of the silicon nitridefilm is increased, the silicon nitride film having uniform density alongthe thickness direction while the upper surface of the wafer W isprevented from being nitrided. On the other hand, when the plasmaintensity is so high that the plasma reaches the upper surface of thewafer W at the initial stage of the film deposition step, the uppersurface of the wafer W is nitrided, and thus excellent flatness isachieved at the boundary between the silicon nitride film and theunderlying layer.

In addition, titanium chloride (TiCl₂) gas and ammonia (NH₃) gas may beused as the first reaction gas and the second reaction gas, therebyforming titanium nitride (TiN) film. In this case, a substrate made ofsilicon is used as the wafer W, and Ar gas or nitrogen gas is used as aprocess gas from which the plasma is generated.

In addition, the film deposition step and the alteration step may beperformed in not only the film deposition apparatus (a so-calledsemi-batch apparatus) shown in FIG. 2 but also a single-wafer apparatus.As shown in FIG. 30, such a single-wafer apparatus is provided with, forexample, a vacuum chamber 1, a susceptor 2 that is provided in thevacuum chamber 1 and on which the wafer W is placed, and a gasshowerhead 200 arranged above the susceptor 2 in order to oppose thesusceptor 2. The showerhead 200 has plural gas ejection holes 201 on thelower surface. In addition, gas supplying lines 202, 203, 204, and 205are connected to corresponding gas conduits (not shown) formed in theshowerhead 200. With this configuration, a first reaction gas, a secondreaction gas, a separation gas (purge gas), and a process gas from whichthe plasma is generated are separately supplied toward the susceptor 2from the corresponding gas ejection holes 201 through the correspondinggas supplying lines 202, 203, 204, and 205 and the corresponding gasconduits. In addition, a high frequency power source 206 is connected tothe showerhead 200, so that the showerhead 200 serves as parallel planarelectrodes together with the susceptor 2. Incidentally, a referencesymbol 210 represents a transfer opening through which the wafer W istransferred into/out from the vacuum chamber 1; a reference symbol 211represents an evacuation port; and a reference symbol 212 represents aninsulating member.

When the film deposition step is performed in the single-waferapparatus, the first reaction gas and the second reaction gas arealternately supplied to the vacuum chamber 1 with purging periodstherebetween. In each of the purging periods, the purge gas is suppliedto the vacuum chamber 1 while the vacuum chamber 1 is evacuated. Whenthe alteration step is performed, after the vacuum chamber 1 is purgedwith the purge gas and evacuated to vacuum, the process gas from whichthe plasma is generated is supplied to the vacuum chamber 1, and thehigh frequency power is supplied across the showerhead 200 and thesusceptor 2. In such a manner, the film deposition step and thealteration step are alternately performed with the purging periodstherebetween.

Next, experiments carried out in order to study the influence of theplasma intensity in the alteration step and their results are explained.

Example 1

First, dependence of the plasma intensity of the plasma on the innerpressure in the vacuum chamber 1 and the high frequency power wasstudied. In this experiment, the batch type experimental apparatus wasused. This apparatus is provided with a vacuum chamber, a susceptorinside the vacuum chamber, and an ICP type plasma source arranged tooppose the susceptor. Distance between the plasma source and the wafer Wis set to 80 mm. After the wafer W was placed on the susceptor and theplasma was irradiated to the wafer W for 180 s, the oxide film thicknessj of the silicon oxide film formed on the upper surface of the wafer Wwas measured. Such an experiment was carried out repeatedly, withdifferent pressures of the vacuum chamber while the high frequency powerwas maintained at 200 W, and with different high frequency powers whilethe inner pressure in the vacuum chamber was maintained at 266 Pa (2Torr)

As a result, it has been found that the plasma intensity can be adjustedby changing the inner pressure in the vacuum chamber, as shown in FIG.31, and by changing the high frequency power, as shown in FIG. 32.

Example 2

Next, shrinkage rates of silicon oxide films are explained. The siliconoxide films used were formed on the wafers W by performing only the filmdeposition step without the alteration step. The shrinkage rates werecalculated using thicknesses of the silicon oxide films before and afterthe alteration step was performed with respect to the silicon oxidefilms at various plasma intensities.

As a result, it has been found as shown in FIG. 33 that the shrinkagerate is in linear proportion with the plasma intensity. This resultindicates that the film properties along the thickness direction can beadjusted by changing the plasma intensity.

Example 3

Next, oxidation of the silicon wafer W by the plasma including O₂ gaswas studied. In this experiment, a bare silicon wafer with the cleanupper surface (or with silicon exposed) and a test silicon wafer with athermal silicon dioxide layer having a thickness of 10 nm were used. Theupper surfaces of the bare silicon wafer and the test silicon wafer withthe thermal silicon dioxide layer are exposed to the plasma fordifferent periods of time while the turntable 2 is rotated in the filmdeposition apparatus explained with reference to FIGS. 2 through 8.

As a result, after the upper surface of the bare silicon wafer wasexposed to the plasma for 10 minutes, a silicon oxide film having athickness of 2.8 nm was formed thereon, as shown in FIG. 34. This resultindicates that the silicon oxide can be formed with a controlledthickness by adjusting the plasma intensity as the thickness isincreased, as explained with reference to FIGS. 21 and 22.

On the other hand, a silicon oxide film having a thickness of only 0.6nm was formed on the thermal silicon dioxide layer on the test siliconwafer, after the test silicon wafer (the thermal silicon dioxide layer)was exposed to the plasma for 10 minutes. When the silicon oxide isformed through the irradiation of the plasma, the silicon oxide is grownthrough the plasma-oxidization of the upper surface of the siliconwafer. Therefore, when the thermal silicon dioxide is formed on theupper surface of the silicon wafer, the plasma cannot penetrate deepinto the silicon wafer, and thus the silicon oxide film having athickness of only 0.6 nm was obtained. In addition, this resultindicates that the plasma can penetrate into the silicon wafer even whenthe thermal silicon dioxide layer is formed on the test silicon wafer.Therefore, it has been confirmed that the plasma can oxidize the uppersurface of the wafer W through the silicon oxide film deposited in thefilm deposition step, while altering the properties of the depositedsilicon oxide film.

While the present invention has been described in reference to theforegoing embodiments, the present invention is not limited to thedisclosed embodiments, but may be modified or altered within the scopeof the accompanying claims.

What is claimed is:
 1. A film deposition apparatus that forms a thinfilm on a substrate by repeating a cycle of alternately supplying pluralkinds of reaction gases to the substrate under vacuum, wherein a firstreaction gas among the plural kinds of the reaction gases reacts with asecond reaction gas among the plural kinds of the reaction gases, thesecond reaction gas being adsorbed on the substrate, thereby to producea reaction product, the film deposition apparatus comprising: asusceptor that is provided in a vacuum chamber and includes a substratereceiving area in which a substrate is placed; an evacuation system thatevacuates the vacuum chamber; plural reaction gas supplying parts thatsupply the corresponding reaction gases to the substrate placed in thesubstrate receiving area; a plasma generation part that generates plasmaincluding a chemical component that reacts with the second reaction gasadsorbed on the substrate, and supplies the plasma to the substrateduring formation of a thin film of the reaction product thereby to alterthe thin film on the substrate; and a controlling part that outputs acontrolling signal in order to change plasma intensity of the plasmathat is generated and supplied to the substrate by the plasma generationpart at a predetermined point of time to a different plasma intensitybefore the predetermined point of time.
 2. The film deposition apparatusof claim 1, wherein the second reaction gas serves as an oxidizing ornitriding gas with respect to the second reaction gas adsorbed on thesubstrate, and wherein the thin film is formed of one of metal oxide,silicon oxide metal nitride, and silicon nitride.
 3. The film depositionapparatus of claim 2, wherein an underlying film of the thin film to beformed thereon includes metal or silicon.
 4. The film depositionapparatus of claim 1, wherein the controlling part changes the plasmaintensity by adjusting at least one of high frequency power supplied tothe plasma generation part and an inner pressure in the vacuum chamber.5. The film deposition apparatus of claim 1, wherein the controllingpart sets the plasma intensity of the plasma that is generated andsupplied to the substrate by the plasma generation part at a firstintensity in an initial stage of forming the thin film, and sets theplasma intensity of the plasma generated and supplied to the substrateby the plasma generation part at a second intensity after the initialstage of forming the thin film.
 6. The film deposition apparatus ofclaim 1, wherein the controlling part sets the plasma intensity of theplasma that is generated and supplied to the substrate by the plasmageneration part at a second intensity in an initial stage of forming thethin film, and sets the plasma intensity of the plasma that is generatedand supplied to the substrate by the plasma generation part at a firstintensity that is lower than the second intensity after the initialstage of forming the thin film.
 7. The film deposition apparatus ofclaim 6, wherein the controlling part sets the plasma intensity of theplasma that is generated and supplied to the substrate by the plasmageneration part at a third intensity that is higher than the firstplasma intensity after setting the plasma intensity of the plasma thatis generated and supplied to the substrate by the plasma generation partat the first intensity.
 8. The film deposition apparatus of claim 1,wherein the plural reaction gas supplying parts and the plasmageneration part are provided at predetermined intervals along acircumferential direction of the vacuum chamber, wherein the filmdeposition apparatus is provided with a rotating mechanism that rotatesthe susceptor around a vertical axis with respect to the plural reactiongas supplying parts and the plasma generation part so that the substratereceiving area of the susceptor passes alternately through areas towhich the plural reaction gas supplying parts supply the correspondingreaction gases, wherein the plasma generation part is arranged so thatthe plasma generated by the plasma generation part is supplied to thesubstrate in one of a first area to which the first reaction gas thatreacts with the second reaction gas adsorbed on the substrate issupplied and a second area located downstream relative to the first areaalong a rotation direction of the susceptor, and wherein the vacuumchamber is provided in order to separate the areas with a separationarea that is located between the areas to which the plural reaction gassupplying parts supply the corresponding reaction gases.
 9. A filmdeposition method that forms a thin film on a substrate by repeating acycle of alternately supplying plural kinds of reaction gases to thesubstrate under vacuum, wherein a first reaction gas among the pluralkinds of the reaction gases reacts with a second reaction gas among theplural kinds of the reaction gases, the second reaction gas beingadsorbed on the substrate, thereby to produce a reaction product, thefilm deposition method comprising steps of: placing a substrate in asubstrate receiving area of a susceptor provided in a vacuum chamber;evacuating the vacuum chamber; alternately supplying plural kinds of thereaction gases to the substrate in the substrate receiving area fromcorresponding reaction gas supplying parts thereby to form a thin filmon the substrate; supplying plasma including a chemical component thatreacts with the second reaction gas adsorbed on the substrate from aplasma generation part to the substrate when the thin film is beingformed, thereby to alter the thin film on the substrate; and changingplasma intensity of the plasma supplied to the substrate, at apredetermined point of time to a different plasma intensity of theplasma that is generated and supplied to the substrate by the plasmageneration part before the predetermined point of time.
 10. The filmdeposition method of claim 9, wherein the first reaction gas serves asan oxidizing or nitriding gas with respect to the second reaction gasadsorbed on the substrate, and wherein the thin film is formed of one ofmetal oxide, silicon oxide metal nitride, and silicon nitride.
 11. Thefilm deposition apparatus of claim 10, wherein an underlying film of thethin film to be formed thereon includes metal or silicon.
 12. The filmdeposition method of claim 9, wherein the plasma intensity is changed byadjusting at least one of high frequency power supplied to the plasmageneration part and an inner pressure in the vacuum chamber in thechanging the plasma intensity.
 13. The film deposition method of claim9, wherein the plasma intensity of the plasma that is generated andsupplied to the substrate by the plasma generation part is set at afirst intensity in an initial stage of forming the thin film, and at asecond intensity that is higher than the first intensity after theinitial stage of forming the thin film, in the changing the plasmaintensity.
 14. The film deposition method of claim 9, wherein the plasmaintensity of the plasma that is generated and supplied to the substrateby the plasma generation part is set at a second intensity in an initialstage of forming the thin film, and at a first intensity that is lowerthan the second intensity after the initial stage of forming the thinfilm, in the changing the plasma intensity.
 15. The film depositionmethod of claim 14, wherein the plasma intensity of the plasma that isgenerated and supplied to the substrate by the plasma generation part isset at a third intensity that is higher than the first plasma intensityafter setting the plasma intensity of the plasma that is generated andsupplied to the substrate by the plasma generation part at the firstintensity, in the changing the plasma intensity.
 16. The film depositionmethod of claim 9, wherein the susceptor is rotated around a verticalaxis with respect to the plural reaction gas supplying parts arranged atpredetermined intervals along a rotation direction of the susceptor sothat the substrate receiving area of the susceptor passes alternatelythrough areas to which the plural reaction gas supplying parts supplythe corresponding reaction gases, in the forming the thin film, whereinthe plasma generated by the plasma generation part is supplied to thesubstrate in one of a first area to which the first reaction gas thatreacts with the second reaction gas adsorbed on the substrate issupplied and a second area located downstream relative to the first areaalong a rotation direction of the susceptor, in the altering the thinfilm, and the film deposition method further comprising supplying aseparation gas from a separation area that is located between the areasto which the plural reaction gas supplying parts supply thecorresponding reaction gases in order to separate the areas.
 17. A filmdeposition method that forms a thin film on a substrate by repeating acycle of alternately supplying plural kinds of reaction gases to thesubstrate under vacuum, wherein a first reaction gas among the pluralkinds of the reaction gases reacts with a second reaction gas among theplural kinds of the reaction gases, the second reaction gas beingadsorbed on the substrate, thereby to produce a reaction product, thefilm deposition method comprising steps of: placing a substrate in asubstrate receiving area of a susceptor provided in a vacuum chamber;evacuating the vacuum chamber; supplying the plural kinds of thereaction gases from corresponding reaction gas supplying parts towardthe susceptor; supplying plasma including a chemical component thatreacts with one of the second reaction gas adsorbed on the substrate andat least apart of the substrate from the plasma generation part towardthe susceptor; and rotating the susceptor around a vertical axis so thatthe substrate receiving area passes alternately through a supplying areato which the second reaction gas is supplied, a reaction area where thefirst reaction gas reacts with the second reaction gas adsorbed on thesubstrate, and a plasma area that is arranged downstream relative to thereaction area along a rotation direction of the susceptor and where theplasma is supplied, wherein the supplying area, the reaction area, andthe plasma area are arranged at intervals along a circumferentialdirection of the vacuum chamber.
 18. A computer readable storage mediumthat stores a computer program to be used in a film deposition apparatusthat forms a thin film on a substrate by repeating a cycle ofalternately supplying plural kinds of reaction gases to the substrate,the computer program including groups of instructions that cause thefilm deposition apparatus to perform the film deposition method of claim9.